1. Field of the Invention
The present invention relates to an optical tomographic image photographing apparatus and a control method therefor.
2. Description of the Related Art
In recent years, an optical coherence tomography (OCT) device, which is capable of acquiring a tomographic image of a fundus, has received attention. One of the reasons therefor is the OCT device enables a noninvasive and high-resolution observation of the tomographic structure of a fundus. Particularly, SD-OCT (spectral domain) devices capable of high-speed and high-sensitive measurement occupy a central position in the market. These SD-OCT devices are increasingly sophisticated by being provided with a fundus camera or a scanning laser ophthalmoscope (SLO).
On the other hand, in order to detect a tiny tumor or other abnormalities by early diagnosis and early treatment, an increase in the image quality of tomographic image is demanded. As a unit for achieving high image quality, there is disclosed a device for causing an OCT beam to follow the movement of an eyeball (Japanese Unexamined Patent Application Publication [Translation of PCT Application] No. 2004-512125). In the invention disclosed in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2004-512125, an OCT device is provided with a device for detecting the movement of an eyeball. It is described that the device tracks an optic papilla of a fundus and controls a tracking scanner in real time to facilitate the acquisition of a tomographic image at a desired place.
There are, however, various movements of an eyeball and can be classified into the following: a micro saccade, which is a fast and linear movement; a drift, which is a slightly slow movement; and a tremor, which is a fast vibration with a small amplitude occurring during drifting. While the moving speed and frequency of the movement depend on each individual, the micro saccade is said to have a speed in the order of several mm/sec, which is an incommensurable speed compared to the drift having a speed in the order of 100 μm/sec. The cycle of the micro saccade is in the order of once or twice per several seconds. The drift continues to move without a break. The tremor is a small movement with an amplitude of 5 μm, though having a cycle in the order of 100 Hz.
Among them, the micro saccade sometimes occurs within the time for photographing a fundus image when detecting the movement of an eyeball by using a fundus image. Moving a scanner on the basis of the fundus image at the time of occurrence of this phenomenon causes the scanner to be moved to an unexpected position. Therefore, it is necessary to detect a sudden eye movement on the basis of the fundus image to prevent such a situation.